Study on the roles of plant growth substances in parthenocarpy of fruit vegetables

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Aimed to clarify the roles of plant growth substances in parthenocarpy of cucumber, var. Chojitsu-ochiai-nigo and Mogami were polinated or not and treated with benzylaminopurine (BA) or naphthaleneacetic acid (NAA) on the day of anthesis, and the mode of fruit growth was analyzed physiologically, histologically and chemically. When the fruit length and fresh weight were analyzed on the basis of their averages, Mogami fruits never induced to grow without polination but its growth was promoted even without polination if treated with BA or NAA. Growth of not-polinated Chojitsu-ochiai-nigo fruits was almost the same as that of polinated ones, but neither BA nor NAA influenced their growth regardless polinated or not. When the growth was analyzed based on frequency distribution of the fruit length, two separated peaks were found in that for Chojitsu-ochiai-nigo. Almost all the polinated fruits belonged to the peak in 10 cm or longer, and half of not-polinated fruits belonged to the peak in 10 cm or longer and other half to the peak in 4-6 cm which was the same as the length of ovary on the day of anthesis. BA and NAA did not influence the positions of the peaks in polinated fruits but the 4-6 cm peak was shifted to 6-10 cm region in not-polinated fruits. These facts suggest that parthenocarpy is all-or-none typed trigger reaction, BA and NAA do not act as the trigger but enhance the growth of not-triggered fruits. Cell number and cell size were measured with the sections cut from paraffined fruits finding that the fruit growth induced by polination and by the treatment with BA was mainly through cell division. The ELISA detected indoleacetic acid (IAA) in Chojitsu-ochiai-nigo at the amount 60 times higher than in Mogami and found the IAA content in the fruits of which growth was induced by parthenocarpy was three orders higher than those not-induced ones suggesting that endogenous auxin may have some roles in regulation of the parthenocarpy.